A device called a pressure type flow controller has been widely used for flow control of gas to be supplied to a chamber of a semiconductor manufacturing facility.
FIG. 5 illustrates an example in the event that processing gas G is supplied into a chamber to form a silicon oxide film using a pressure type flow controller FCS. A specified quantity Q of processing gas G is supplied to a pressure-reduced chamber C by using a vacuum pump Vp, and a quantity Q of processing gas G is discharged to a wafer H on the supporting device I through a gas discharger D.
On the other hand, the afore-mentioned pressure type flow controller FCS utilizes the relation that “when a critical condition P1>approx. 2×P2 is maintained, a quantity Q of gas passing through an orifice L is determined only by gas pressure P1 on the upstream side of the orifice, and is represented by the formula Q=CP1 (where C is a constant dependent on the bore of the orifice L and gas temperature)”, thus a quantity Q on the downstream side of the orifice L being able to be held at a desired set value by regulating the afore-mentioned pressure P1 with a control valve CV.
With FIG. 5, P0 designates supply pressure of processing gas G, Pm a manometer, F a filter, CPU a central processing unit, Qs an input signal for a flow rate setting, and Qe an output signal for control of the flow rate.
A pressure type flow controller itself has been publicly disclosed with the TOKU-KAI-HEI No.8-338546, the TOKU-KAI-HEI No.11-63265 and others. Therefore, detailed explanations are omitted herewith.
With the afore-mentioned flow controller FSC, it becomes an essential condition that, as stated above, gas pressure P1 on the upstream side of the orifice and gas pressure P2 on the downstream side of the orifice are within the afore-mentioned critical condition. The drawback is that the flow control cannot be performed because the critical expansion pressure condition is not satisfied, for example, when gas pressure P2 on the downstream side of the orifice rises more than gas pressure P1 on the upstream side of the orifice.
Another drawback is that flow control accuracy is lowered in reality when P1/P2 reaches closer the limit value of the afore-mentioned critical pressure condition with the rise of pressure P2 on the downstream side of the orifice. Thus limiting the flow control range capable of being used when pressure P2 on the downstream side rises.
As above, various drawbacks are seen with the control of the gas flow rate by the pressure type flow controller when pressure P2 on the downstream side of the orifice L rises. However, the gas supply method to a chamber by using the said pressure type flow controller FCS allows the gas flow control with the high degree of accuracy easily to be performed, and makes it possible that a pressure regulating device with the high degree of accuracy at the gas supply source is not required to be provided, thus allowing considerable reductions of the costs in a gas supply facility, to achieve excellent, practical effects.
On the other hand, a silicon wafer with a larger external diameter has been used for semiconductor manufacturing in recent years. In the case of the wafer H with an external diameter of 300 mmφ, for example, there are required separate adjustments for supply quantities of processing gas to the center part and the peripheral (edge) part respectively.
As a measure to handle the matter, processing gas can be supplied to the afore-mentioned center part and edge part respectively by providing separate branch supply lines GL1 and GL2 as shown in FIG. 6, thus being able to supply processing gas G without any difficulties from a gas supply source S with specified quantities Q1 and Q2 even with gas supply lines GL1 and GL2 wherewith a pressure type flow controller FCS.
However, to supply gas using gas supply lines GL1 and GL2 both of which are equipped with a pressure type flow controller FCS1 and FCS2 independently into a chamber invites a rise in installation costs as well as upsizing of a semiconductor manufacturing facility, and is also found to be time-consuming for its maintenance. For these reasons, the method is undesirable.
To solve these problem, as shown in FIG. 7, it is found desirable that the method wherewith flow rate Q1 and Q2 of branch gas supply lines GL1 and GL2 are controlled by branching two gas supply lines GL1 and GL2 from a pressure type flow controller FCS, and regulating flow rate control valves V1 and V2 equipped with the gas supply lines GL1 and GL2 respectively is employed.
Among the general-purpose pressure type flow controllers FCS for a gas supply facility presently used, ones with flow rate control characteristics capable of being used within the range of 0˜100 Torr of pressure P2 on the downstream side of the orifice under optimum conditions have been widely employed in general. Accordingly, with these pressure type flow controllers FCS, the flow rate control range is considerably limited when pressure P2 on the downstream side of the orifice exceeds approximately 100 Torr, as described above, from the point of flow rate accuracy.
For example, let's assume that processing gas G of a flow rate Q=300SCCM is to be supplied to a chamber C through supply lines GL1 and GL2 at flow rates of Q1=130 SCCM and Q2=170 SCCM in FIG. 7. With a gas supply facility not equipped with a pressure type flow controller FCS, firstly flow rate control valves V1 and V2 are closed, and next, the flow rate of processing gas is set to Q=300 SCCM, and then flow rates Q1 and Q2 can be adjusted to the set value by regulating the degree of opening of control valves V1 and V2 automatically or with reference of a flow meter (not illustrated).
However, in the event that a pressure type flow controller FCS is used for a flow controller of the gas supply facility as illustrated in FIG. 7, both control valves V1 and V2 are first placed in a state of being fully closed, and a flow rate Q (300 SCCM) of the pressure type flow controller FCS is set. Then, the degree of opening of both control valves V1 and V2 are adjusted to the flow rate Q1 (130 SCCM) and Q2 (170 SCCM) for branch supply lines GL1 and GL2. This, however, finds it difficult to control the flow rates accurately and quickly.
The reasons are that there is a possibility that the values of P1/P2 are out of the threshold value of critical pressure conditions of the afore-mentioned pressure type flow controller FCS due to the rise of pressure P2 on the upstream side of both control valves V1 and V2 when opening of V1 and V2 are small, thus resulting in that the control flow rate Q with the pressure type flow controller FCS becomes vastly different from the set flow rate of Q=300 SCCM.
To solve the afore-mentioned difficulties, inventors of the present invention have applied for a patent, the TOKU-GAN-HEI No. 2002-161086 by developing a method to supply gas while dividing gas into a chamber from a gas supply facility.
This is a completely new idea: of switching from the conventional and well-worn method wherewith gas from a gas supply facility is supplied while dividing for being controlled, that is, flow rate control valves V1 and V2 provided with branch supply lines are put in a state of fully or near-fully closing, and then, both flow rate control valves V1 and V2 are gradually opened, while with the new method both flow rate control valves V1 and V2 are made to be in a state of fully or near-fully opening, and then, both flow rate control valves V1 and V2 are regulated to the direction of closing step by step for the opening adjustment, thus making it possible that while a total flow quantity Q is controlled at the high degree of accuracy with the pressure type flow controller FCS, flow rates Q1 and Q2 are controlled by the pressure type division quantity controllers FV1 and FV2 provided with branch supply lines GL1 and GL2 at a desired flow rate ratio Q1/Q2 accurately and quickly.
With the method, there will be no possibility that pressure P2 on the downstream side of the orifice of the pressure type flow controller FCS rises sharply at the time of being divided even with processing gas from a gas supply facility provided with a pressure type flow controller FCS, thus making it possible that the total quantity Q is accurately controlled at a desired flow rate value Q regardless of the flow control while dividing by means of a pressure type division quantity controllers FV1 and FV2. Accordingly, excellent characteristics of a pressure type flow controller FCS can be utilized, thus making it possible that the flow division control while dividing is performed accurately and quickly, and also with a plurality of flow rate ratios Q2/Q1.
As stated above, the method employed in the TOKU-GAN-HEI No. 2002-161086 made it possible that flow rates Q1 and Q2 of branch supply lines GL1 and GL2 are regulated at a desired flow rate ratio Q1/Q2 accurately and quickly. However, on the other hand, the method made the control complicated because it employed two pressure type division quantity controllers FV1 and FV2 beside a pressure type flow controller FCS for regulating pressure on both sides, thus inviting another problem of facility costs becoming higher.    Patent Literature 1: TOKU-KAI-HEI No. 8-338546 Public Bulletin    Patent Literature 2: TOKU-KAI-HEI No. 11-63265 Public Bulletin